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Home >> Mercedes Benz >> 1974 >> 450SEL >> Repair and Diagnosis (Single Page) >> Engine Performance >> Engine Control Systems >> Exhaust Emissions System - Exhaust Gas RECIRCULATION >> Testing >> EGR System >> 1975-76 280 Models
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1975-76 280 Models

  1. Remove Brown/Purple vacuum hose from EGR valve. Turn ignition on and blow air into hose. Place transmission in Drive, Park and Neutral position. In Park and Neutral, hose should be open. In Drive, hose should be closed. If not, check vacuum hose routing.
  2. The Brown vacuum hose from vacuum booster should be attached to center connection of Brown switchover valve. The Brown/Purple vacuum hose to EGR valve should be on outer connection of switchover valve. If vacuum hose routing is correct, check relay box.
  3. Remove Green vacuum hose and Brown vacuum hose (at connection D) from carburetor. See Figure. Connect Brown vacuum hose in place of Green vacuum hose on carburetor.
  4. Start engine and place transmission in Park, Neutral, and Drive. With transmission in Park or Neutral, engine should run smoothly. With transmission in Drive, engine should run rough or stall.
  5. If engine does not run as specified, check vacuum hoses on vacuum booster for damage and proper routing. Also check EGR valve. Remove Brown/Purple vacuum hose at Brown switchover valve.
  6. Start engine and remove Green vacuum hose from Green switchover valve. Connect Brown/Purple hose with Green hose. Engine should run rough or stall. If not, replace EGR valve. If engine runs rough or stalls, replace vacuum booster.
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